1. Field of the Invention
The present invention relates to a sensor device employing passive infrared and microwave sensor technology, and a method for using the same. More particularly, the present invention relates to a method and apparatus employing a motion or occupancy sensor which includes a passive infrared sensor and microwave sensor in conjunction with logic circuitry to control activation and deactivation of devices such as lighting circuits.
2. Description of the Related Art
Motion sensor switches, such as Model 1WS-ZP-M and Model 1WS-ZP-277V motion sensor switches manufactured by Hubbell, Inc., include a motion sensor, such as a passive infrared detector (PIR), and an ambient light level sensor, such as a photocell. Other motion sensor switches are described in U.S. Pat. Nos. 5,821,642 to Nishihira et al., 5,699,243 to Eckel et al., and 4,874,962 to Hermans, the entire contents of each being incorporated herein by reference.
Motion sensor switches of this type can be used, for example, as an occupancy detector which shuts off lights in a room when the sensor detects that no one is present in the room, and turns on the lights in the room when a person enters the room. A motion sensor switch also can be used, for example, as a motion sensor for an alarm system.
During operation, the motion sensor of the motion sensor switch monitors an area, such as an office, conference room in a building, or a home, for the presence of movement. Specifically, the motion sensor detects a change in the infrared energy radiating from regions in the area monitored by different sensing lobes of the PIR detector, which generally have a pass band within the 8-14 xcexcm infrared range. If a person enters the monitored area, the person changes the amount of infrared energy being detected by the PIR detector. Therefore, the magnitude of the signal output by PIR detector, which is representative of the amount of detected infrared energy, will change. A motion sensor circuit in the motion sensor switch processes this signal, and provides a signal to a controller indicating that the amount of infrared energy received by the infrared detector has changed.
The controller interprets the signal provided by the motion sensor circuit, along with the signal provided by ambient light level sensor. If the signal provided by ambient light level sensor indicates that the ambient light in the monitored area is low (e.g., very little natural light is present in the monitored area), the control circuit will turn on or increase the brightness of the lights in the monitored area. However, if the signal provided by ambient light level sensor indicates that the ambient light in the monitored area is sufficient (e.g., due to sunlight, etc.), the control circuit may not turn on or brighten the lights, or may only brighten the lights slightly. In either event, control of the lights is based on the signals provided by the motion sensor and ambient light level sensor.
Motion sensor switches of this type also typically include a delay timing adjustment device, such as a potentiometer, which can be manually adjusted to set the delay time during which the lights should remain on after all occupants have left the monitored area. For example, if the delay timing adjustment device is adjusted to a 30-second setting, when all occupants leave and remain out of the monitored area for a period of time exceeding 30 seconds, the circuit of the motion sensor turns off the lighting load in the monitored area to conserve energy.
The motion sensor switches described above which employ only a PIR detector are generally suitable for their intended purpose. However, because PIR detectors detect infrared energy, these types of sensors can be susceptible to false triggering by other devices in the monitored area, such as computers, heating vents, and the like, that emit infrared energy.
In an attempt to minimize these false triggerings, a sensor has been developed that uses a PIR detector in conjunction with an ultrasonic detector. An example of a sensor employing PIR and ultrasonic detector technologies is described in U.S. Pat. No. 5,189,393 to Hu, the entire content of which is incorporated herein by reference. As can be appreciated by one skilled in the art, an ultrasonic sensor detects movement of an object. Accordingly, a sensor employing a PIR detector and an ultrasonic detector can include logic circuitry which requires detection of heat and movement in the monitored area to provide a switching signal to, for example, activate a lighting circuit.
Although a sensor employing both PIR and ultrasonic detector technology may be more accurate than a sensor employing only a PIR detector or only an ultrasonic detector, this type of sensor does have certain disadvantages. For example, ultrasonic detectors are sensitive to air movements such as air turbulence. Therefore, if a sensor employing an ultrasonic detector is used to monitor a room in a building, the air flow from the ventilation system of the building can cause a false triggering of the detector. Moreover, ultrasonic detectors are also sensitive to acoustic noise. Hence, noisy vehicles such as street sweepers and the like operating outside the building can cause false triggering of the ultrasonic detectors in the sensors in the building.
Other types of dual technology sensors are known for use in burglar alarm systems. For example, a Sentrol(trademark) Model 2T40 motion sensor employs a microwave sensor technology, such as microwave impulse radar (MIR) technology and PIR technology. However, although it is necessary for these types of burglar alarm systems to accurately detect when an intruder has initially entered a monitored area to signal an alarm, it is not necessary for these types of systems to detect with extreme accuracy the continued presence of the intruder in the monitored area, or to detect when the intruder has left the monitored area. Therefore, these types of detectors have not been employed in conjunction with circuitry suitable for use as lighting control circuitry.
Accordingly, a need exists for an improved dual technology sensor which is capable for use as an efficient and accurate motion sensor for controlling lighting circuitry and does not suffer from the disadvantages of conventional sensors.
An object of the present invention is to provide an accurate and reliable dual technology motion or occupancy sensor.
Another object of the present invention is to provide a motion or occupancy sensor including a PIR sensor and a microwave sensor.
A further object of the present invention is to provide a method of using a dual technology motion or occupancy sensor, such as a motion or occupancy sensor including a PIR sensor and a microwave sensor.
These and other objects of the present invention are substantially achieved by providing a sensor and method for controlling a lighting circuit in a monitored area, employing an infrared energy sensor, a microwave energy sensor, and a controller. The infrared energy sensor is adapted to output an infrared energy detection signal indicative of detection or non-detection of infrared energy, and the microwave energy sensor is adapted to output a microwave energy detection signal indicative of detection or non-detection of microwave energy. The controller is adapted to output a control signal to control activation and deactivation of the lighting circuit in response to a condition of the infrared energy detection signal and a condition of the microwave energy detection signal.
Specifically, when the controller is controlling the lighting circuit to be in an inactive state and determines based on the infrared energy detection signal and microwave energy detection signal that the monitored area has become occupied, the controller activates the lighting circuit to turn the lights in the monitored area on. The controller maintains the lights in the on condition as long as the infrared energy detection signal or the microwave energy detection signal indicate that the monitored area is occupied. However, when both the infrared energy detection signal and the microwave energy detection signal indicate to the controller that the monitored area has been unoccupied for a period of time, the controller deactivates the lighting circuit to turn the lights in the monitored area off. The controller can determine the conditions of the microwave and infrared energy detection signals as indicating occupancy or vacancy of the monitored area by comparing the signals to respective threshold levels that the controller can calibrate as appropriate. The controller can also be configured to deactivate the lighting circuit that is in the active state when either the microwave energy detection signal or the infrared energy detection signal fails to indicate detection of occupancy in the monitored area for a period of time. The controller can also perform filtering on the microwave and infrared energy signals to avoid erroneous occupancy detection.